Usually, bars which must be machined with a lathe are fed to the machine tool by a feeder which is adapted to contain a plurality of bars in order to provide optimum automation of the production cycle.
The bar, after insertion in the feeder, is located within a respective guide and is subjected to an axial translational motion by a pusher, which can be associated with the end portion of such bar. The pusher pushes the bar out of the feeder (through an appropriately provided opening in the front face of said feeder) until such bar is inserted in the mandrel of the lathe.
The pusher is designed to retain the rear end of the bar, also in order to recover the portion of the bar that is not machined and carry it toward the feeder for expulsion.
For this purpose, the pusher is normally provided with an elastic element, typically provided as an elastic ring, which is adapted to retain the rear end of the bar. The outside diameter of such elastic element may be greater than the diameter of the bar, and therefore the guiding elements located between the feeder and the lathe, and possibly in the mandrel of the lathe, may have a substantially larger inside diameter than the bar in order to allow the passage of the pusher and of the element for gripping the rear end of the bar.
The radial play produced between the bar and the elements for guiding between the feeder and the lathe, within the mandrel, and possibly also within the feeder, is such as to allow oscillations of the bar which are limited only by the rigidity of the clamping member of the grip element (collet) of the lathe mandrel, by the rigidity of the bar itself, by the rear grip of the elastic element of the pusher, and possibly by the feeder guiding elements (if they are of the type which can be adjusted dynamically to the diameter of the bar), but allows more or less substantial vibrations caused by the rotation of the bar during the machining of the front end of said bar.
These vibrations can have a negative effect on the machining of the part, in the form of finish defects or even dimensional defects, and in general limit the rotation rate to levels at which the effects can be considered negligible.